The present invention relates to a spray-coating gun.
Accordingly, the invention relates in particular to a spray-coating gun for spray coating objects with coating powder, wherein the spray-coating gun has a coating powder spray head at its front end region for spraying coating powder and a coating powder connection as well as at least one compressed gas connection at its opposite rear end region. Coating powder can be supplied to a coating powder channel extending to the coating powder spray head via the coating powder connection of the spray-coating gun. Compressed gas, particularly compressed air, can be supplied to a compressed gas channel extending to the front end region of the spray-coating gun via the at least one compressed gas connection of the spray-coating gun.
The invention relates in particular to spray-coating guns for coating powder conveyed pneumatically in a compressed air flow. The coating material is sprayed through a material discharge outlet of the coating powder spray head at the front end region of the spray-coating gun. The material discharge outlet can for example be formed by a material channel outlet with or without a transverse deflector (impact head or the like), by a nozzle or by a rotating atomizer element.
The coating material is preferably electrostatically charged by static electricity and/or by a high voltage of more than 1000 volts, for example a voltage in the range of between 10,000 and 140,000 volts, in order to thereby achieve better adhesion to the preferably grounded object to be coated and to reduce waste.
The spray-coating gun according to the invention can be a manual or an automatic powder spraying device comprising a spray nozzle or a rotating atomizer.
When the spray-coating gun is in operation, a coating powder line is connected to the gun's coating powder connection, by means of which the coating powder to be sprayed is supplied to the spray-coating gun for example from a powder reservoir or a powder container.
There are different ways in which the coating powder to be sprayed can be supplied to the spray-coating gun and the coating powder conveyed through the coating powder line.
In particular, a powder dispensing device, usually also called a powder injector, can be used for this purpose. With such a powder injector, the coating powder is pumped out of a powder container by means of conveying compressed air and fed to the coating powder connection of the spray-coating gun. In so doing, a mixture of conveying compressed air and powder flows through a powder channel of a diffuser inside the powder injector, whereby additional dosing air is added to the powder/conveying air mixture via the diffuser in order to obtain a defined total air flow.
Fresh powder is supplied to the powder container as needed via a fresh powder line from a supplier container with which the powder supplier supplies fresh powder to the powder user. The powder forms a compact mass in the supplier container. In contrast to that, the coating powder in the powder container is to be in a fluidized state so that it can be for example aspirated by the suction effect of a powder injector and supplied to the spraying device in a flow of compressed air.
On the other hand, however, it is also conceivable to use at least one powder pump to supply the coating powder to be sprayed to the spray-coating gun and to convey the coating powder through the coating powder line.
For example, the EP 1 551 558 A1 printed publication describes a powder pump having a first powder chamber and a second powder chamber arranged parallel to the first powder chamber. The powder chambers of this known prior art powder pump are respectively limited on both the inlet-side as well as the discharge-side by a mechanical pinch valve arrangement. It is thereby specifically provided for the powder hoses connected to the respective powder chambers to be able to be deformed by a mechanically operated punching tool in the inlet-side or discharge-side area of the powder pump respectively in order to squeeze or open the hose section as needed. The powder chambers of the known pump each further have a gas-permeable filter element. A negative pressure can be separately set in each powder chamber by means of a vacuum connection, in consequence of which coating powder can be sucked into the powder chamber via the intake-side end region of the respective powder chamber. The pinch valve provided at the intake-side end region of the powder chamber is then subsequently closed and the pinch valve provided at the discharge-side end region of the powder chamber opened. Upon application of positive pressure in the powder chamber, the coating powder previously sucked into the powder chamber is then discharged back out of the powder chamber via the discharge-side end region.